Afterwards committee members described him as "a credible witness", with a number adding his evidence had been "very worthwhile".

Dressed in his official garda uniform, he went into the committee chamber alone around 2pm and did not bring any legal advisor with him.

The hearing took place despite the objections of the the Garda Commissioner, Martin Callinan.

The committee has yet to decide whether a transcript of his testimony will be kept for the record.

After the hearing ended, committee chairman John McGuinness said Sgt McCabe had given the committee a unique insight into the way the fixed charge system worked at an operational level.

Mr McGuinness outlined that the session was in private and was conducted within strict legal parameters that had been set down in legal advice given to the committee.

“No garda officer was named, third parties who had tickets cancelled were not named, no instance was cited where a member of the force, a member of the public, or any outside body was accused of acting wrongly," he said.

"The evidence of Sgt McCabe focused on his experience as a member of the Garda Siochana and the concerns he had around the penalty point system, which led him to give evidence.

"In that regard the evidence focused on the systems, practices and procedures of the penalty point system and patterns in the cancellation of points."

Mr McGuinness thanked Sgt McCabe for his evidence and noted the issues he had raised will now be the subject of further investigation by the Garda Siochana Ombudsman Commission.